This invention relates generally to electrical control devices and in particular to those having means operable generally for adjusting an air gap therein, a method of adjusting an air gap in an electrical control device, and a method of operating adjusting means for an electrical control device.
In the past electrical control devices, such relays or circuit breakers or the like for instance, means, such as an armature, was adapted for attraction from a generally at-rest position through an air gap into magnetic holding engagement with an electromagnet or the like upon the energization thereof. The extent of the air gap or travel between the attraction means or armature from its at-rest position into magnetic holding engagement determines, at least in part, the energy level or pick-up voltage of the electromagnet necessary for attracting the armature into magnetic holding engagement therewith. The armature was usually resiliently loaded to determine, at least in part, the energy level or drop-out voltage of the electromagnet at which it was unable to hold the armature in magnetic engagement. Of course, various and sundry means or mechanisms were provided in the prior art for adjusting the air gap between the electomagnet and the armature thereby to adjustably predetermine the pick-up voltage and also for adjusting the resilient force opposing the magnetic attraction between the armature and the electromagnet thereby to adjustably predetermine the drop-out voltage. One such prior art electrical control device is disclosed in the D. E. Moran U.S. Pat. No. 2,831,934 issued Apr. 22, 1958.
In this patent, as well as other similar prior art disclosures, the pick-up voltage of the disclosed relay was adjusted by turning a generally flat head metal screw threaded into the frame of the relay. As the screw head was moved in or out relative to the relay frame, it generally linearly drove a part of an armature to effect pivotal movement of the armature for adjusting the at-rest position thereof with respect to an electromagnet of the relay to adjustably alter the air gap therebetween. Undoubtedly, this patent discloses many salient and important features; however, it is believed that one of the disadvantageous or undesirable features encountered in utilizing this particular type of prior art adjusting means, as well as others, was its limited applicability with respect to different sized or rated electrical control devices. For instance, screws of different lengths may be required in different rated electrical control devices to cover the required adjusting range thereof and prevent the screws from touching an electrical coil of the electromagnet or other electrically hot parts of the relay.
Another disadvantageous or undesirable feature of adjusting means for at least some of the other prior art electrical control devices is believed to be that separate adjusting screws, such as that discussed above, were necessary to effect the desired force and air gap adjustments.
With respect to still further other prior art electrical control devices, a cam was rotatably engaged with the armature to effect the desired resilient force and air gap adjustments for such past electrical control devices. However, one of the disadvantageous or undesirable features of the past rotatable, cam type, adjusting means is believed to be that its rotatable adjusting movement was too coarse to achieve the rather fine adjustment necessary for predetermining the pick-up and drop-out voltages of electrical control devices as may be encountered in a production line assembly for instance.